The present invention relates to a magnetic disk apparatus fitted with a magnetic head slider and is especially adapted for a magnetic disk apparatus fitted with a magnetic head slider of the thermally assisted type which locally reduces the coercive force of a magnetic disk by a heating element and makes a magnetic recording at this location using a recording element.
To realize a magnetic disk apparatus of high recording density, it is necessary to make small recording particles on a magnetic disk. And, to permit small magnetization patterns to exist stably, it is necessary to enhance the coercive force of the magnetic disk. However, it has become more difficult to rewrite small recording particles of high coercive force without erasing data in adjacent tracks, using only recording elements.
To solve this problem, a magnetic recording method known as thermally assisted recording has been proposed. This thermally assisted magnetic recording adopts a magnetic disk whose coercive force at room temperature is higher than conventional. During recording, the magnetic disk is locally and momentarily heated. The moment the coercive force decreases, magnetic recording is made. The thermally assisted magnetic recording is adapted for vertical (perpendicular) magnetic recording, as well as for longitudinal magnetic recording. It is said that this is a technique necessary to dramatically improve the recording density of a magnetic disk apparatus in future. As a method of heating a magnetic disk, a Joule heating system of a simple structure using heating elements (heater) is being discussed along with the laser-heating type.
A cited problem with the thermally assisted magnetic recording is that the yaw angle varies when a magnetic head slider carrying record/playback elements thereon is driven by a rotary actuator and moves arcuately over a magnetic disk.
This point is described using FIG. 13. If recording is not done in a short period of the order of 10 microseconds from heating of a medium, heat will propagate to the surroundings and the temperature will drop. Therefore, it is impossible to make recording after waiting for several milliseconds in which the disk rotates once. Accordingly, a heating element 4 and a recording element 2 must be disposed on a straight line of a track (data row arrayed in a circumferential direction) on which recording is to be made. If the magnetic head slider 1 is placed in position using the rotary actuator 16, in a case where the recording element 2 and heating element 4 are over the same track in a track T1 lying in some radial position of the magnetic head slider 1, the center lines of movement of the heating element 4 and recording element 2 deviate at a track T2 in a different radial position. They are not located over the same track. If so, it is impossible to prewarm the area of the magnetic disk 1 to be recorded by the heating element 4. Since playback is done after being placed in position again, no problems will take place if the radial positional relation between the playback element 3 and other element deviates.
In order to solve the problem of the track deviation between the heating element and the recording element due to variation of the yaw angle as described so far, four countermeasures have been heretofore proposed. First, as shown in FIG. 14, a linear actuator is adopted such that the heating element and recording element are kept over a track regardless of whether the track is the outer track T1 or the inner track T2. Secondly, as shown in FIG. 14, the dimensions of the heating element are increased such that the heating element and recording element are kept over a track regardless of whether the track is the outer track T1 or the inner track T2. Thirdly, as shown in FIG. 14, a means for moving the heating element is provided to maintain the heating element and recording element over a track regardless of whether it is the outer track T1 or the inner track T2. Fourthly, a plurality of heating elements are provided and electrically switched in a corresponding manner to variation in the yaw angle. Thus, the heating elements and recording element are kept over the track regardless of whether it is the outer track T1 or the inner track T2. The third and fourth countermeasures are disclosed in JP-A-2004-134051 (Patent Reference 1).
The first countermeasure is a countermeasure capable of certainly solving the track deviation between the heating element and the recording element. However, a linear actuator is expensive and large in size. It is quite difficult to use it in the present magnetic disk that is inexpensive and small in size.
With respect to the aforementioned second countermeasure, power consumption generating heat within the magnetic head slider 1 increases. If generation of heat within the magnetic head slider 1 is large, temperature rise of the playback element portion affects the life and reliability of the playback element. Another problem is that the contact possibility between the magnetic head slider 1 and magnetic disk is affected by thermal expansion known as thermal protrusion.
The aforementioned third countermeasure involves a complex structure and has a movable portion. Therefore, there remain elements to be developed in the future. Furthermore, this third countermeasure needs 2 lead wires of 1 system for driving, in addition to 6 lead wires of 3 systems for recording, playback, and heating. An increase in the number of lead wires results in an increased price. Additionally, there is the problem that it is difficult to mount them. Especially, in a small-sized slider (having a length of 0.85 mm, 0.7 mm, and a thickness of 0.23 mm) of a standard known as a femto slider, an area that can be used for electrical connection with a suspension is small. Realistically, only 6 lead wires of 3 systems can be mounted at best. It is quite difficult to mount 8 lead wires of 4 systems as in the third countermeasure.
With the aforementioned fourth countermeasure, 7 or more lead wires including record/playback elements in the case of two heating elements are necessary in order to supply power supply for all of plural heating elements independently from outside the slider into the slider. In the case of three heating elements, 8 or more lead wires are necessary. Therefore, the fourth countermeasure has the problem that an increase of the number of lead wires increases the price and makes it more difficult to mount them. Especially, it is quite difficult to mount them to a femto slider. Patent Reference 1 makes a mention of a configuration having a circuit that switches the used heating element inside a magnetic head slider. A lead wire or interconnect for a signal for selecting a heating element is connected with the switching circuit independently. Mounting of 6 lead wires of 3 systems is not achieved.